In the sequence A - B - C, compound A undergoes reaction with dilute NaOH at low temperature (NaOH in excess) to give B. Compound B then reacts with OH⁻/heat (aldol-type condensation) to give C. Compound B gives a positive Tollens test and a positive iodoform test. Which of the following

Question

In the sequence A -> B -> C, compound A undergoes reaction with dilute NaOH at low temperature (NaOH in excess) to give B. Compound B then reacts with OH⁻/heat (aldol-type condensation) to give C. Compound B gives a positive Tollens test and a positive iodoform test. Which of the following could be a possible structure for A?

Accepted Answer

CH3CHO (acetaldehyde). B gives positive Tollens (is an aldehyde or alpha-hydroxy aldehyde) and positive iodoform (has CH3-CH(OH)- or CH3CHO group). If A = CH3CHO, then with excess dilute NaOH at low T, aldol condensation gives 3-hydroxybutanal (an alpha-hydroxy aldehyde) as B, which gives positive Tollens and positive iodoform. Then B under OH⁻/heat gives the crotonaldehyde C via aldol dehydration. This is consistent with all given conditions.

Solution

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